isn't being addicted to something when the person "craves", enjoys or feels like they must have the X substance? For example - they take a pill to primarily feel the high or pleasurable sensation - not to simply control a body acting up in pain/twitching/etc.

Needing to take a medication (either sporadically or regularly) to control physical symptoms/issues is to me treating a medical problem. Taking something simply for the pleasurable feeling is addiction. *just my personal opinion*